The present invention relates to a heater for vehicles. More specifically, the present invention pertains to a heater that has a rotor and viscous fluid in its housing and generates heat by the rotor rotation shearing the viscous fluid. The heat generated by the rotor is transferred to another fluid such as a coolant that circulates through the housing.
A heater using the drive force of a vehicle engine is described, for example, in a German Unexamined Patent Publication No. 3832966. The heater will now be described with reference to FIG. 9. The heater has a housing 71 including a heating chamber 72 and a ring-shaped water jacket 73 around the heating chamber 72. An annular housing 87 is provided between the heating chamber 72 and the water jacket 73. A reservoir 74 is located adjacent to the heating chamber 72 in the housing 71. Engine coolant flows into the water jacket 73 through an inlet passage 88 and then flows to a heat exchanger of the vehicle through an outlet passage 89. A certain amount of viscous fluid 79 is charged in the heating chamber 72 and the reservoir 74. The viscous fluid occupies about half the volume of the reservoir 74.
A middle wall 75 separates the heating chamber 72 and the reservoir 74. The middle wall 75 has a supply passage 83 for supplying the viscous fluid 79 from the reservoir 74 to the heating chamber 72. A partition wall 75 has a return passage 84 for returning the viscous fluid 79 from the heating chamber 72 to the reservoir 74. The supply passage 83 is opened and closed by a lever 86 that has a bimetal plate spring 85. This adjusts the supply amount of the viscous fluid 79 to the heating chamber 72, thus adjusting the level of heat generation.
A drive shaft 76 is rotatably supported in the rear of the housing 71. A rotor 77 is rigidly attached to one end of the drive shaft 76 to integrally rotate with the drive shaft 76. A pulley 78 is fixed to the other end of the drive shaft 76. The pulley 78 is connected to an engine (not shown) by a belt.
When the engine rotates the rotor 77, the viscous fluid is sheared between an inner surface 81 of the heating chamber 72 and a shearing surface 80 of the rotor 77. This generates heat. The heat generated in the heating chamber 72 is transferred through the partition wall 87 to the coolant flowing in the water jacket 73. Then, the coolant is supplied to a heat exchanger of the vehicle for warming the passenger compartment.
When the viscous fluid is relatively cool, the bimetal plate spring 85 does not press the lever 86 to the supply passage 83. Accordingly, the supply passage remains open, permitting the supply of the viscous fluid 79 from the reservoir 74 to the heating chamber 72.
In such heaters, it is important to reduce the torque load on the rotor 77 when the rotor 77 first starts to rotate. When the engine stops during the operation of the heater, the rotor 77 stops and the return of the viscous fluid from the heating chamber 72 to the reservoir 74 is stopped. Therefore, a substantial amount of the viscous fluid 79 remains in the heating chamber 72.
When the rotor 77 starts to rotate again, the remaining viscous fluid 79 applies a significant torque load to the rotor 77. In other words, a great torque load is applied to the engine through the rotor 77 and the belt. This causes noise, torque shock, slippage of the belt, and wear on the parts of the heater. Also, since the viscous fluid 79 occupies about half the volume of the reservoir 74, the viscous fluid 79 is likely to be oxidized by the air in the reservoir 74. This deteriorates the quality of the viscous fluid 79 and heat generating capacity of the heater.